1. Technical Field
The present invention relates to signal processing, and more particularly to transponder aggregator-based optical loopback in a multi-degree reconfigurable optical add/drop multiplexer (MD-ROADM).
2. Description of the Related Art
A reconfigurable optical add/drop multiplexer (ROADM) is an important network element in wavelength division multiplexing (WDM) optical networks and has been widely deployed in long haul and metro WDM networks in recent years. A ROADM enables the flexible adding and dropping of any or all WDM channels at the wavelength level without manual configuration or the costly and power-consuming optical-electrical-optical (O-E-O) switches. In mesh or meshed ring optical networks, multi-degree ROADMs (MD-ROADMs) also provide cross-connection functions of WDM signals among different paths, so they are also called wavelength cross-connects (WXCs). Here a degree refers to an input/output pair from a certain direction.
Conventional MD-ROADMs have the issues of colored operation (each add/drop port is restricted to a fixed predetermined wavelength), directional operation (the add/drop operations at each degree are separate, i.e. the node cannot share the transponders among different degrees), and contention operation (blocking occurs if the same wavelength from multiple degrees need to be dropped simultaneously).